The invention relates to a polarizing element having a first layer for influencing the direction of at least one of the polarization components of an unpolarized beam incident on the element, which components have different directions of polarization.
The invention also relates to an image projection device in which at least one of the polarizers surrounding the image display panel is implemented as the first or the second layer of a polarizing element in accordance with the invention, and to an image projection device in which the first polarizer or the image display panel, together with the polarizer and the analyzer, is implemented as a polarizing element in accordance with the invention.
To polarize an unpolarized beam, use may be made of all kinds of polarizers. One of the best known types is an absorbing polarizer which absorbs the unwanted direction of polarization. A drawback of such a polarizer is that approximately 50% of the intensity of the unpolarized beam is lost. Moreover, when a high-power radiation source is used, for example in image projection devices, the polarizer may be considerably heated, which may be harmful for the material from which the polarizer is made and will lead to degradation of the polarizer. To eliminate the harmful effect of this heating as much as possible, expensive cooling systems are to be provided which also detrimentally influence the compactness of the device.
Another type of polarizer is a polarizing element of the type described in the opening paragraph and is known, for example from British Patent Application GB 2 166 562. The polarizing element described in this Application consists of a layer in which areas comprising a liquid crystalline material and areas comprising a transparent isotropic material alternate with each other in a direction located in the plane of the layer. The structure thus formed may be considered as a diffraction grating. The major axis of the molecules of the liquid crystalline material is directed parallel to the grooves of the diffraction grating. By providing electrodes on the substrates between which the diffraction grating is formed, the orientation of the liquid crystalline molecules, and hence the direction of the diffraction to which light incident on the element is subjected, may be changed. Such a polarizer passes the desired direction of polarization and refracts the unwanted direction of polarization from the light path.
The risk of damage of this type of polarizer is much smaller because the unwanted light is no longer absorbed by the polarizer. However, such a polarizer still has the drawback that substantially half the intensity of an unpolarized beam incident on the element is lost because the unwanted direction of polarization is refracted from the original beam. When such an element is used as a polarizer in a device in which a high brightness of the images is desirable, as in, for example an image projection device, the use of a high-power light source is still desirable. However, such a light source consumes a relatively large amount of current and dissipates relatively much heat in the device so that cooling measures are still to be taken.